Transducer head with spacer material made of stainless steel

ABSTRACT

An electromagnetic transducer head comprises a plurality of magnetic tracking circuits with screening means between the individual circuits and in order to overcome the adverse effects of differential wear as between the magnetic circuit pole pieces and the intermediate spacer material used is made of stainless steel in place of the conventional non-magnetic materials such as brass, aluminium and plastics materials. The tracking circuits may be fitted into slots in a stainless steel blank or a blank of conventional non-magnetic material may be used with stainless steel spacers fitted in between the tracking circuits.

United States Patent 1 1 A 11.11 3,864,753

Becker et al. 1 Feb. 4, 1975 1 TRANSDUCER HEAD WITH SPACER 2,895,0157/1959 Zenel et a1. 179/1002 c MATERIAL MADE OF STAINLESS STEEL3,053,940 9/1962 Scarbrough 179/1001 C 3,064,333 11/1962 Kristiansen179/1002 C 5] n ento o er Sidney Becker, y Eric 3,316,359 4/1967Sakasegawa.... 179/1002 c Frank Painter, Shepperton; Gerrard 3,404,24210/1968 Girdner 179/ 100.2 C Charles Rickard, Woodham, all of EnglandPrimary Examiner-Alfred H. Eddleman [73] Assignee: Gresham Infomag Ltd.,Weybridge, Attorney, Agent, or Firm-Young & Thompson England [22] Filed:May 9, 1973 [57] ABSTRACT [21] Appl. No.: 358,698

An electromagnetic transducer head comprises a plurality of magnetictracking circuits with screening Foreign Application ity ata meansbetween the individual circuits and in order to May 9, 1972 GreatBritain 21638/72 overcome the adverse effects of differential wear asbetween the magnetic circuit pole pieces and the in- [52] U.S. Cl360/121, 360/122, 360/125 termediate spacer material used is made ofstainless [51] Int. Cl Gllb S/12, G1 lb 5/22, G1 lb 5/26 steel in placeof the conventional non-magnetic mate- [58] Field of Search l79/l00.2 C,100.2 MD; rials such as brass, aluminium and plastics materials.

340/1741 F; 346/74 MC; 360/119, 120, 121, The tracking circuits may befitted into slots in a stain- 122 less steel blank or a blank ofconventional nonmagnetic material may be used with stainless steel [56]References Cited spacers fitted in between the tracking circuits.

UNITED STATES PATENTS 2,839,614 6/1958 Merrill 179/1002 c 10 Clams} 5Draw F'gures if 1 Z PATEHTEU FEB 75 SHEET 1 BF 2 FIG. 2.

TRANSDUCER HEAD WITH SPACER MATERIAL MADE OF STAINLESS STEEL FIELD OFTHE INVENTION This invention relates generally to electromagnetictransducer heads, and is more particularly concerned with tape recordingand/or playback heads.

DESCRIPTION OF THE PRIOR ART In the manufacture of conventionalrecording/- playback heads a body blank of brass, aluminium, or asuitable plastics material is grooved to hold a plurality of magneticcircuits comprising pole pieces each carrying an electrical winding. Thebody blank is additionally grooved between each of the grooves carryingthe magnetic circuits, and into these additional grooves are fittedscreens, for example of a magnetic alloy such as Mumetal. With thisconventional arrangement the magnetic circuits located in their groovesare spaced from each other by land portions on the body blank, withthese land portions having the screens slotted therein. This means thatthe magnetic circuits are bounded on each side by the material such asbrass or aluminium or plastics material which constitutes the bodyblank.

This conventional construction has been found to have considerabledisadvantages when used with magnetic tape due t the differential wearrate as between the magnetic circuit pole pieces and the intermediatespacer material such as brass, aluminium, or plastics material forexample. This differential wear has the effect of causing the surface ofthe magnetic circuit pole pieces over which the tape moves to becomeconcave. In addition to degrading the quality of the recording on thetape, this also causes the coating of the tape to be damaged, resultingin tape wear and the deposition of oxide particles on to the transducinghead.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide an improved transducing head which substantially eliminatesdifferential wear between the magnetic circuit pole pieces and theintermediate spacing material, which reduces the overall wear rate by afactor of to times for example as compared with the use of conventionalmaterials, and which also causes less damage to the associated taperesulting in a cleaner head and less tape wear.

This is achieved by using stainless steel, at least in part, as thematerial of the head between the individual tracking circuits over whichthe tape passes for the transfer of information.

Also in accordance with the present invention there is provided anelectromagnetic transducer head comprising a body blank having a surfaceover which a tape is adapted to pass, a plurality of magnetic trackingcircuits supported in said blank each with a pole piece face flush withsaid surface, and screening means between the respective trackingcircuits, characterised in that the land areas between the trackingcircuits and over which the tape is adapted to pass are at leastpartially of stainless steel.

This use of stainless steel has the somewhat surprising result ofachieving the objects set out above and provides a greatly improvedtransducing head.

In one embodiment the body blank is of stainless steel and is grooved toreceive said tracking circuits and screening means.

In another embodiment the body blank is of nonmagnetic material and hasinserts at least partially of stainless steel fitted therein between thetracking circuits.

Preferably, the land area between each pair of adjacent trackingcircuits is of stainless steel adjacent to each tracking circuit withsaid screening means substantially midway between the tracking circuits.

A description of certain preferred embodiments in accordance with theinvention will now be given by way of example and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the two bodyparts of a singlegap recording head with a gap spacer indicatedschematically therebetween;

FIG. 2 is a side view of one of the body parts of FIG. 1 taken to theline AA of FIG. 1;

FIG. 3 is a sectional view of one of the body parts of FIG. 1 takenalong the line BB of FIG. 1;

FIG. 4 is a schematic illustration of a modified embodiment oftransducing head in accordance with the invention; and,

FIG. 5 is a schematic representation of a modified form of spacer foruse with the embodiment shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows schematically thetwo basic body parts of a recording/playback transducer head which whenassembled together and secured by dowel pins and screws have a gapspacer positioned therebetween. The two body parts are indicatedgenerally at 10 and 11, the gap spacer at 12, and an associated magnetictape is shown at 13, the arrows indicating its direction of movementover the head. Considering the body part 10 for example, (the body part11 is the same in construction and is therefore not separatelydescribed) this comprises a body blank which is first provided with aplurality of parallel slots 14 into which screens 16 of a magneticalloy, such as Mumetal for example, are fitted. Wider but shallowerslots 18 are then out between each pair of screen slots 14 and receiveindividual magnetic tracking circuits as shown more clearly in FIGS. 2and 3. The slots 14 and 18 are cut directly into the inside face 19 ofthe body blank.

Each of the magnetic tracking circuits comprises a pole piece 20 of amagnetic material such as Mumetal having a pole tip 22 and a heel 24.Each pole piece 20 is formed by a stack of laminations and has a winding26 formed around the central smaller cross-section portion. The coil 26is connected to terminal pins on a terminal board 28.

In accordance with the present invention the body blank 10 (and the bodyblank 11 also), which has conventionally been made of brass, aluminium,or a plastics materiahis made of stainless steel. The slots 14 and 18are machined into the stainless steel body blank with the result thatthe pole tips 22 of the pole pieces 20 are separated by land areas 30 ofstainless steel divided by the screens 16. It has been found that thisreplacement of the conventional materials for the lands 30 between thetracking circuits by stainless steel has a most beneficial effect on thewear of the head, and in particular on the differential wear between thepole tips 22 and the lands 30. It also results in less damage to thetape 13 and in a reduction in the deposition of oxide particles from thetape on the head.

Although the beneficial effects obtained with the present invention areobtained with stainless steels quite generally, a stainless steel alloyof the following composition has been found particularly preferable:

Carbon-0.12%

Manganese2% Silicon l% Nickel-8 to ll% Chromiuml7 to 20% and theremainder iron.

FIG. 4 shows an alternative embodiment of transducer head in accordancewith the present invention which has the advantage as compared with theembodiment shown in FIGS. 1 to 3 that it is not necessary to machine theslots 14 and 18 in a stainless steel blank. The body blank 10 of FIG. 4is made of brass, aluminium, a plastics material, or any other suitableeasily machinable material including those which are conventionallyused. Instead of machining the deep narrow grooves 14 and the relativelydeep wider grooves 18 in the inside face 19 of the body blank, arectangular cross-section portion of the blank is first removed to adepth indicated by reference numeral 40 and then a plurality ofrelatively shallow grooves 41 are machined in this recessed body blank.The individual magnetic tracking circuits comprising the pole pieces 20are fitted between the grooves 41. Between the pole pieces 20 and fittedinto the grooves 41 between each pair of pole pieces are spacers 46.Each of the spacers 46 is formed by the combination ofa plurality ofrectangular laminations of stainless steel, preferably the stainlesssteel alloy of the composition referred to above. In order to providethe necessary screening between the individual magnetic trackingcircuits each of the spacers 46 includes a screen 48 of Mumetal forexample, the screen preferably being at the centre of the spacer. Thescreen 48 is of the same depth and height as the spacer laminations andmay have a lateral dimension transversely of the direction of movementof the tape 13 approximately equal to one third of the overall lateralthickness of the spacer 46.

FIG. S-shows a modified form of spacer for use in an embodiment similarto that shown in FIG. 4 where, in order to accommodate the thickness ofthe windings 26 on the pole pieces 20 each spacer 50 comprises a Mumetalscreen 52 which is provided with stainless steel spacer laminations 53only at its ends adjacent to the pole tip 22 and heel 24 of the polepieces.

A separate, or additional, improvement is obtained in certainconfigurations of magnetic circuit and spacer size ratios, by replacinga number of magnetic circuit laminations with stainless steellaminations, for example every fifth lamination of the stack.

By variations and combinations of the embodiments described above thewear rate of the parts of the magnetic transducer head can be controlledfor individual circumstances of utilisation to provide desired wearcharacteristics.

Although the invention as described above'has been given with referenceto a single-gap recording/playback head it should be clearly understoodthat the invention may be applied to double-gap heads and indeed quitegenerally to electromagnetic transducer heads of various differenttypes.

It should also be understood that the particular relative dimensions andcombinations of elements shown in V the drawings and described above arenot to be considered as limiting the scope of the invention. Forexample, although in FIG. 4 the screen 48 is shown as a plate setcentrally in the spacer 46 an effective magnetic screen can be producedby other combinations of magnetic material and stainless steellaminations stacked together.

We claim:

1. A multi-track tape electromagnetic transducer head comprising a bodyhaving a surface over which a tape is adapted to pass, a plurality ofrespective magnetic tracking circuits supported in said body and eachhaving a pole piece having a face flush with and forming part of saidsurface, each said face contacting a respective longitudinally extendingarea of said tape for the transfer of information between the associatedmagnetic and the associated area of the tape, characterised in that saidsurface is at least partially of stainless steel between said magnetictracking circuits.

2. In a multi-track electromagnetic transducer head comprising a bodyblank having a surface over which a tape is adapted to pass in contactwith said surface, a plurality of respective magnetic tracking circuitssupported in said blank and each having a pole piece having a face flushwith and forming part of said surface, each said face contacting arespective longitudinally extending area of said tape for the transferof inform ation between the associated magnetic circuit and theassociated area of the tape, screening means between the respectivetracking circuits, and land areas between the tracking circuits andforming parts of said surface, the improvement comprising said landareas being formed of stainless steel.

3. A transducer head as claimed in claim 2, in which the body blank isof stainless steel and is grooved to receive said tracking circuits andscreening means, said land areas comprising parts of said body blank.

4. A transducer head as claimed in claim 2, in which the body blank isof non-magnetic material and has inserts at least partially of stainlesssteel fitted therein between the tracking circuits and forming said landareas.

5. A transducer head as claimed in claim 2, in which the land areabetween each pair of adjacent tracking circuits is of stainless steeladjacent to each tracking circuit with said screening meanssubstantially midway between the tracking circuits.

6. A transducer head as claimed in claim 5, wherein the thickness ofsaid screening means transversely of the direction of movement of thetape is substantially equal to the thickness of the stainless steel oneach side thereof.

7. A transducer head as claimed in claim 4, in which each insertcomprises a screening plate co-extensive with the adjacent trackingcircuits and portions of stainless steel on each side of the screeningplate adjacent to said pole piece faces with a gap therebelow toaccommodate windings on the tracking circuit pole pieces.

8. A transducer head as claimed in claim 4, in which said stainlesssteel is constituted by laminations stacked together.

6 Manganese 2% Silicon 1% Nickel 8 to 11% Chromium 17 to 20% and theremainder iron.

1. A multi-track tape electromagnetic transducer head comprising a bodyhaving a surface over which a tape is adapted to pass, a plurality ofrespective magnetic tracking circuits supported in said body and eachhaving a pole piece having a face flush with and forming part of saidsurface, each said face contacting a respective longitudinally extendingarea of said tape for the transfer of information between the associateDmagnetic and the associated area of the tape, characterised in that saidsurface is at least partially of stainless steel between said magnetictracking circuits.
 2. In a multi-track electromagnetic transducer headcomprising a body blank having a surface over which a tape is adapted topass in contact with said surface, a plurality of respective magnetictracking circuits supported in said blank and each having a pole piecehaving a face flush with and forming part of said surface, each saidface contacting a respective longitudinally extending area of said tapefor the transfer of information between the associated magnetic circuitand the associated area of the tape, screening means between therespective tracking circuits, and land areas between the trackingcircuits and forming parts of said surface, the improvement comprisingsaid land areas being formed of stainless steel.
 3. A transducer head asclaimed in claim 2, in which the body blank is of stainless steel and isgrooved to receive said tracking circuits and screening means, said landareas comprising parts of said body blank.
 4. A transducer head asclaimed in claim 2, in which the body blank is of non-magnetic materialand has inserts at least partially of stainless steel fitted thereinbetween the tracking circuits and forming said land areas.
 5. Atransducer head as claimed in claim 2, in which the land area betweeneach pair of adjacent tracking circuits is of stainless steel adjacentto each tracking circuit with said screening means substantially midwaybetween the tracking circuits.
 6. A transducer head as claimed in claim5, wherein the thickness of said screening means transversely of thedirection of movement of the tape is substantially equal to thethickness of the stainless steel on each side thereof.
 7. A transducerhead as claimed in claim 4, in which each insert comprises a screeningplate co-extensive with the adjacent tracking circuits and portions ofstainless steel on each side of the screening plate adjacent to saidpole piece faces with a gap therebelow to accommodate windings on thetracking circuit pole pieces.
 8. A transducer head as claimed in claim4, in which said stainless steel is constituted by laminations stackedtogether.
 9. A transducer head as claimed in claim 1, in which eachtracking circuit comprises a stack of laminations together forming apole piece, with a proportion of said laminations being of stainlesssteel.
 10. A transducer head as claimed in claim 1, in which thestainless steel has the composition: Carbon 0.12% Manganese 2% Silicon1% Nickel 8 to 11% Chromium 17 to 20% and the remainder iron.